Terminal, base station, and communication method for reference signals with phase shift indexes

ABSTRACT

In the multiple short sequence based SRS, multiple items of sequence data having a short sequence length corresponding to a partial band are used for transmitting SRS in discontinuous bands. In the multiple short sequence based SRS, a terminal specifies a frequency domain to be used for transmitting a reference signal using predetermined sequence data, applies a phase shift index associated with the specified frequency domain to the reference signal, and transmits the reference signal to which the phase shift index is applied by using the specified frequency domain.

TECHNICAL FIELD

The present disclosure relates to a terminal, a base station, and acommunication method.

BACKGROUND ART

In the standardizing of the fifth-generation mobile communication system(5G), a new radio access technology (NR (New RAT)), which does notnecessarily have backward compatibility with LTE/LTE-Advanced, which isthe current system, is being discussed in 3GPP.

In LTE/LTE-Advanced, a terminal (may also be called “UE (UserEquipment)”) transmits a Sounding Reference Signal (hereinafter called“SRS”) in a radio resource allocated by a base station (may also becalled “eNB” or “gNB”). The base station measures the quality of thereceived SRS to estimate the uplink channel quality in the SRS transmitband. LTE/LTE-Advanced also states that SRS is transmitted in acontinuous band to regulate CM (Cubic Metric)/PAPR (Peak-to-AveragePower Ratio).

In NR, simultaneously transmitting of SRS in multiple partial bands 100(that is, transmitting SRS in discontinuous bands) as shown in FIG. 14is being discussed (see NPL 1, for example).

In NR, using of a wider system band than that in LTE/LTE-Advanced isbeing examined. If a wide bandwidth is used for transmitting SRS,terminals located near cell edges become short of transmission power.Discontinuous transmission of SRS by using partial bands of the systemband may make it possible to transmit SRS in a wide band while usingless transmission power of terminals. This allows a base station toquickly estimate the uplink channel quality in a wide band.

The multiple short sequence based SRS that uses multiple items ofsequence data having a short sequence length corresponding to a partialband to transmit SRS in discontinuous bands is being examined (see NPL2, for example). As the SRS code sequence, Zadoff-Chu (ZC) sequence dataused for SRS in LTE/LTE-Advanced is used. The sequence length of ZCsequence data is set to be a length corresponding to one partial band100. To perform simultaneous transmission in multiple partial bands,plural items of ZC sequence data are used to transmit SRS.

In the multiple short sequence based SRS, in each partial band 100,different cyclic shift (CS) indexes (or phase shift indexes) fordifferent terminals are set. With this configuration, if the partialbands 100 have the same size, orthogonalization of SRSs, which aretransmitted from plural terminals having different transmit bands, canbe conducted in units of partial bands 100 (see FIG. 14). The multipleshort sequence based SRS thus implements high flexibility in performingSRS frequency scheduling.

CITATION LIST Non Patent Literature

NPL 1: R1-1613470, CATT and others, “WF on SRS transmission for NR”,RAN1#87, November 2016

NPL 2: R1-1611808, LG and others, “Considerations on NR SRS design”,RAN1#87, November 2016

SUMMARY OF INVENTION

In the multiple short sequence based SRS, in order to allow pluralterminals to implement flexible orthogonalization of SRSs by using CS,it is necessary to inform each terminal of a CS index used for eachpartial band 100 (see FIG. 15). This increases overhead for supplying CSindex information.

One non-limiting embodiment of the present disclosure facilitatesproviding a terminal, a base station, and a communication method thatare capable of reducing overhead of signaling for supplying CS indexinformation in the multiple short sequence based SRS.

A terminal according to an embodiment of the present disclosure includesa circuit and a transmitter. The circuit specifies a frequency domain tobe used for transmitting a reference signal using predetermined sequencedata and applies a phase shift index associated with the specifiedfrequency domain to the reference signal. The transmitter transmits thereference signal to which the phase shift index is applied by using thespecified frequency domain.

A base station according to an embodiment of the present disclosureincludes a receiver and a circuit. The receiver receives a referencesignal using predetermined sequence data in a specific frequency domain.The circuit compares a base signal and the reference signal with eachother. The base signal is a signal to which a phase shift indexassociated with the specific frequency domain is applied.

A communication method according to an embodiment of the presentdisclosure includes: specifying a frequency domain to be used fortransmitting a reference signal using predetermined sequence data andapplying a phase shift index associated with the specified frequencydomain to the reference signal; and transmitting the reference signal towhich the phase shift index is applied by using the specified frequencydomain.

A communication method according to an embodiment of the presentdisclosure includes: receiving a reference signal using predeterminedsequence data in a specific frequency domain; and comparing a basesignal and the reference signal with each other. The base signal is asignal to which a phase shift index associated with the specificfrequency domain is applied.

It should be noted that these general or specific embodiments may beimplemented as a system, a device, a method, an integrated circuit, acomputer program, a storage medium, or any selective combinationthereof.

According to an embodiment of the present disclosure, it is possible toreduce overhead of signaling for supplying CS index information in themultiple short sequence based SRS.

Additional benefits and advantages of an embodiment of the presentdisclosure will become apparent from the specification and drawings. Thebenefits and/or advantages may be individually obtained by the variousembodiments and features of the specification and drawings, which neednot all be provided in order to obtain one or more of such features.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the configuration of a terminal according to anembodiment of the disclosure.

FIG. 2 illustrates the configuration of a base station according to anembodiment of the disclosure.

FIG. 3 is a diagram for explaining how a partial band and RU aredefined.

FIG. 4 illustrates the configuration of a base station in accordancewith a first embodiment.

FIG. 5 illustrates the configuration of a terminal in accordance withthe first embodiment.

FIG. 6 illustrates an operation of the terminal according to the firstembodiment.

FIG. 7 illustrates an operation of the base station according to thefirst embodiment.

FIG. 8 illustrates CS calculation method 1.

FIG. 9 illustrates an example of SRS allocation used for CM evaluation.

FIG. 10 illustrates the simulation results of CM evaluation.

FIG. 11 illustrates combinations of CS indexes that increase CM.

FIG. 12 illustrates the allocation of CS indexes according to CS indexcalculation method 3.

FIG. 13 illustrates the allocation of CS indexes according to CS indexcalculation method 4.

FIG. 14 is a diagram for explaining the multiple short sequence basedSRS.

FIG. 15 is a diagram for explaining code orthogonalization using CS inunits of partial bands.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described below in detailwith reference to the drawings. In the following description, whenreferring to the same group of elements by distinguishing them from eachother, reference numerals, such as “CS group 342A” and “CS group 342B”,may be used. When referring to the same group of elements withoutdistinguishing them from each other, part of a reference numeral commonto the elements, such as “CS group 342”, may be used. The number may berepresented by “#”.

In the present disclosure, in the multiple short sequence based SRS, thefrequency resource unit which corresponds to the sequence length of oneitem of code sequence (such as ZC sequence) data is called a resourceunit (RU). One RU is constituted by one or more resource blocks (RBs). Acontinuous band including one or more RUs for transmitting SRS is calleda partial band. The partial band size and the RU size may be changed inaccordance with the cell, the service type of NR (eMBB, URLLC, mMTC), orthe carrier frequency. In the embodiments, a description will be given,assuming that the RU size and the partial band size are equal to eachother. However, as shown in FIG. 3, the size of a partial band 120 maybe larger than that of a RU 110.

In the present disclosure, RU numbers are assigned in the followingmanner, for example. In a grid of RUs divided from the system band bythe RU size, numbers are sequentially assigned to the RUs in the orderof frequency.

Overview of Communication System

A communication system according to each embodiment of the disclosureincludes a base station 10 and a terminal 12.

FIG. 1 is a block diagram illustrating the configuration of the terminal12 according to the embodiments of the disclosure. In the terminal 12shown in FIG. 1, a circuit 13 specifies a frequency domain to be usedfor transmitting a reference signal using predetermined sequence data,and applies the phase shift index associated with the specifiedfrequency domain to the reference signal. A transmitter 72 transmits thereference signal to which the phase shift index is applied by using thespecified frequency domain.

FIG. 2 is a block diagram illustrating the configuration of the basestation 10 according to the embodiments of the disclosure. In the basestation 10 shown in FIG. 2, a receiver 20 receives a reference signalusing predetermined sequence data in a specific frequency domain. Acircuit 11 applies the phase shift index associated with the specificfrequency domain to the reference signal.

First Embodiment

The configuration of the base station 10 and that of the terminal 12 inthe multiple short sequence based SRS will be described below.

Configuration of Base Station

FIG. 4 is a block diagram illustrating the configuration of the basestation 10 according to this embodiment in the multiple short sequencebased SRS. In FIG. 4, the base station 10 includes an antenna 21, thereceiver 20, a demodulator-decoder 22, a SRS extractor 24, a qualityestimator 26, a scheduler 28, a replica generator 30, a CS indexcalculator 32, a SRS resource storage 34, a SRS control signal generator36, a modulator-coder 38, and a transmitter 40. The functions of the SRSextractor 24, the quality estimator 26, and the replica generator 30 maybe included in the circuit 11 shown in FIG. 2.

The receiver 20 executes receive processing, such as down-conversion andA/D conversion, on a radio signal received from the terminal 12 via theantenna 21. The receiver 20 then outputs the signal subjected to receiveprocessing to the demodulator-decoder 22.

The demodulator-decoder 22 demodulates and decodes the signal receivedfrom the receiver 20. The demodulator-decoder 22 then outputs thedemodulated and decoded signal to the SRS extractor 24.

The SRS extractor 24 extracts SRS from the signal received from thedemodulator-decoder 22, based on SRS resource information received fromthe SRS resource storage 34. The SRS extractor 24 outputs the extractedSRS to the quality estimator 26.

The SRS resource information is information required for transmittingSRS by the terminal 12. For example, the SRS resource informationincludes information concerning code sequence data, such as the RUnumber, RU size, and CS offset value. The base station 10 is not alwaysrequired to supply all the items of information in the SRS resourceinformation. The base station 10 may inform the terminal 12 of part ofthe SRS resource information, such as the RU size, in advance, asinformation based on a cell unit.

The SRS resource storage 34 stores the SRS resource information sent tothe terminal 12. The SRS resource information sent to the terminal 12 isoutput from the scheduler 28.

The CS index calculator 32 calculates a CS index for each RU in a SRSallocated band, based on the RU number and the CS offset value includedin the SRS resource information received from the SRS resource storage34. The CS index calculator 32 outputs the calculated CS index for eachRU to the replica generator 30. Details of the calculation method for CSindexes by using the RU numbers will be discussed later.

The replica generator 30 identifies the RU size based on the SRSresource information received from the SRS resource storage 34, andgenerates a replica signal corresponding to the RU size by using SRScode sequence data, such as ZC sequence data. Based on the CS index foreach RU received from the CS index calculator 32, the replica generator30 applies a corresponding CS (that is, phase shift) to the generatedreplica signal so as to generate a replica signal to which the CS isapplied. The replica generator 30 outputs the replica signal to whichthe CS is applied to the quality estimator 26. The replica signal may becalled a base signal.

The quality estimator 26 performs correlation calculation to compare theSRS extracted by the SRS extractor 24 and the replica signal to whichthe CS is applied output from the replica generator 30 so as to estimatethe quality in the uplink channel from the terminal 12 to the basestation 10. This estimation result will be called the quality estimationresult. The correlation calculation is performed for each RU, that is,for each code sequence length. The quality estimator 26 outputs thequality estimation result to the scheduler 28.

The scheduler 28 conducts data scheduling (MCS setting, frequencyresource allocation, and transmission power control), based on thequality estimation result received from the quality estimator 26. Thescheduler 28 determines SRS resource information for each terminal 12 bytaking the frequency allocated to the data into consideration. Thescheduler 28 then outputs the determined SRS resource information to theSRS control signal generator 36 and the SRS resource storage 34.

The SRS control signal generator 36 generates a control signal forsupplying the SRS resource information received from the scheduler 28 tothe terminal 12. The SRS control signal generator 36 outputs thegenerated control signal to the modulator-coder 38.

The modulator-coder 38 modulates and codes the control signal receivedfrom the SRS control signal generator 36 and outputs the control signalto the transmitter 40.

The transmitter 40 executes transmit processing, such as D/A conversion,up-conversion, and amplification, on the signal received from themodulator-coder 38. The transmitter 40 then transmits the radio signalsubjected to transmit processing to the terminal 12 via the antenna 21.

Configuration of Terminal

FIG. 5 is a block diagram illustrating the configuration of the terminal12 according to this embodiment in the multiple short sequence basedSRS. In FIG. 5, the terminal 12 includes an antenna 61, a receiver 60, ademodulator-decoder 62, a CS index calculator 64, a SRS generator 66, aSRS band setter 68, a modulator-coder 70, and the transmitter 72. Thefunctions of the SRS band setter 68 may be included in the circuit 13shown in FIG. 1.

The receiver 60 executes receive processing, such as down-conversion andA/D conversion, on a signal received via the antenna 61. The receiver 60then outputs the signal subjected to receive processing to thedemodulator-decoder 62.

The demodulator-decoder 62 demodulates and decodes the signal receivedfrom the receiver 60 and extracts SRS resource information transmittedfrom the base station 10 from the demodulated and decoded signal. Thedemodulator-decoder 62 then outputs the extracted SRS resourceinformation to the CS index calculator 64 and the SRS band setter 68.

The SRS band setter 68 maps SRS received from the SRS generator 66 ontothe RU number included in the SRS resource information. The SRS bandsetter 68 outputs a signal generated by mapping SRS onto the RU numberto the modulator-coder 70.

The CS index calculator 64 performs processing similar to that of the CSindex calculator 32 of the base station 10. That is, the CS indexcalculator 64 calculates a CS index for each RU, based on the RU numberand the CS offset value included in the SRS resource information. The CSindex calculator 64 outputs the calculated CS index to the SRS generator66.

The SRS generator 66 generates SRS by using code sequence (ZC sequence)data having a sequence length corresponding to the RU size included inthe SRS resource information. The SRS generator 66 applies cyclic shift(phase shift) based on the CS index calculated for a corresponding RU bythe CS index calculator 64 to the generated SRS. The SRS generator 66outputs the SRS to which the cyclic shift is applied to the SRS bandsetter 68.

The modulator-coder 70 modulates and codes the signal received from theSRS band setter 68, and outputs the modulated and coded signal to thetransmitter 72.

The transmitter 72 executes transmit processing, such as D/A conversion,up-conversion, and amplification, on the signal received from themodulator-coder 70. The transmitter 72 then transmits the radio signalsubjected to transmit processing to the base station 10 via the antenna61.

Operations of Base Station and Terminal

Operations of the base station 10 and the terminal 12 configured asdescribed above will be described below in detail.

FIG. 6 is a flowchart illustrating an operation of the terminal 12. FIG.7 is a flowchart illustrating an operation of the base station 10.

The terminal 12 specifies a RU (that is, a frequency domain) fortransmitting a reference signal (ST100). The terminal 12 applies thephase shift index associated with the specified RU to the referencesignal (that is, a signal including SRS) (ST102). The terminal 12 thentransmits the reference signal to which the phase shift index is appliedto the base station 10 by using the specified RU (ST104).

The base station 10 receives a reference signal in a specific RU fromthe terminal 12 (ST120). The base station 10 then applies the phaseshift index associated with this specific RU to the reference signal togenerate a base signal (ST122), and compares the reference signalreceived from the terminal 12 and the base signal to which the phaseshift index is applied with each other (ST124). As a result of comparingthe reference signal and the base signal, the base station 10 estimatesthe quality of the uplink channel from the terminal 12 to the basestation 10.

CS Index Calculation Method

Details of methods for calculating CS based on the RU number by the CSindex calculator of each of the terminal 12 and the base station 10 willbe described below in detail.

CS Index Calculation Method 1

FIG. 8 illustrates CS calculation method 1.

In CS calculation method 1, the frequency resource RU number and the CSindex are uniquely associated with each other, and the base station 10supplies a CS offset value to each terminal 12. In this case, the basestation 10 supplies different CS offset values to the terminals 12 whichmultiplex SRSs regardless of the number of partial bands for eachterminal 12.

Based on the RU number of each partial band and the CS offset value, thebase station 10 and the terminal 12 calculate the CS index for acorresponding RU number. The base station 10 may dynamically inform theterminal 12 of the CS offset value by using DCI (Downlink ControlInformation) or semi-statically inform the terminal 12.

In a row 202 of a table 200 shown in FIG. 8, CS index “0” is uniquelyassociated with RU#0, CS index “1” is uniquely associated with RU#1, . .. , and CS index “4” is uniquely associated with RU#4. The base station10 has already informed UE#0 of CS offset “1” and also informed UE#1 ofCS offset “3”. When transmitting SRS in RU#4, UE#0 adds CS offset “1”,which is assigned to UE#0, to CS index “4” associated with RU#4 so as tocalculate cyclic shift index (phase shift index) “5” for SRS. Whentransmitting SRS in RU#4, UE#1 adds CS offset “3”,which is assigned toUE#1, to CS index “4” associated with RU#4 so as to calculate cyclicshift index (phase shift index) “7” for SRS. Different cyclic shiftindexes are applied to SRS of UE#0 and SRS of UE#1 to be transmitted inthe same RU#4, so that the base station 10 can distinguish SRS of UE#0and SRS of UE#1 from each other.

In this manner, by uniquely associating the frequency resource RU numberand the CS index with each other, the base station 10 merely informs theterminal 12 of the CS offset value without the need to supply the CSindex for each partial band to the terminal 12. It is thus possible toreduce overhead of signaling from the base station 10 to the terminal12.

Instead of the base station 10 informing the terminal 12 of the CSoffset value, the CS offset value may be calculated from the ID (RNTI(Radio Network Temporary ID), for example) of the terminal 12.

Calculating the CS offset value from the ID of the terminal 12eliminates the need for the base station 10 to inform the terminal 12 ofthe CS offset value. This can reduce overhead of signaling from the basestation 10 to the terminal 12 to be even smaller. In this case, the basestation 10 conducts scheduling so that terminals 12 having different CSoffset values can allocate SRSs to the same RU.

As described above, according to this embodiment, by uniquelyassociating the frequency resource RU number and the CS index with eachother, it is possible to reduce overhead of signaling for supplying CSindex information in the multiple short sequence based SRS.

Second Embodiment

As discussed above, the use of CS calculation method 1 makes it possibleto reduce overhead of signaling for supplying CS index information.

In the multiple short sequence based SRS, however, CM or PAPR may becomehigher depending on the combination of CS indexes used for RUs.

FIG. 9 illustrates an example of SRS allocation used for CM evaluation.

In FIG. 9, the number of partial bands is “4”, ZC sequence number is“1”, RU size is 4 RBs (1 RB=12 subcarriers), partial band interval is 4RBs, and RUs for transmitting SRS are RU#0, RU#2, RU#4, and RU#6.

FIG. 10 is a graph 300 illustrating the simulation results of CMevaluation by using the combinations of all CS indexes in the SRSallocation in FIG. 9.

CM of OFDM data is 4.0 dB. The graph 300 shows that about 5% of thecombinations of CS indexes make CM of SRS higher than that of OFDM data.

FIG. 11 is a table 320 illustrating an example of combinations of CSindexes that make CM particularly high among the combinations of all theCS indexes used for RUs.

When the allocation patterns of CS indexes to RUs come under thefollowing cases A through D, as shown in the example of the table 320 ofFIG. 11, CM becomes high.

-   -   Case A: The same CS index is used for all RUs (or all partial        bands).    -   Case B: CS indexes used for adjacent RUs (or adjacent partial        bands) are monotonically changed.    -   Case C: The same CS index is used for the first half (lower        frequency) or the second half (higher frequency) of RUs (or        partial bands).    -   Case D: The same CS index is used for most (¾ or higher ratio        according to the evaluation conditions) of all RUs (or all        partial bands).

In a second embodiment, CS index calculation methods 2 through 4 thatcan reduce the occurrence of the above-described cases will bediscussed. In the second embodiment, the configurations of the basestation 10 and the terminal 12, the configuration in which the CS indexand the frequency resource RU number are uniquely associated with eachother, and the configuration in which the base station 10 suppliesdifferent CS offset values to terminals 12 that multiplex SRSs in thesame band regardless of the number of partial bands of each terminal 12are similar to those of the first embodiment.

The CS index calculation methods 2, 3, and 4 are different regarding howthe RU number and the CS index are associated with each other. The CSindex calculation methods 2, 3, and 4 will be discussed below.

CS Index Calculation Method 2

In the CS index calculation method 2, the CS index is randomlyassociated with the RU number.

A random CS index to be set for each RU number may be defined by using apredetermined pattern table in advance in accordance with the cell unitor the system specifications. Alternatively, a random CS index to be setfor each RU number may be calculated by using predetermined apseudorandom number according to the following equation 1.CS(m,n)=mod(PN(m)+Δ(n),N _(CS))  (Equation 1)

In equation 1, m is a RU number, n is a terminal number, N_(CS) is themaximum number of CS (N_(CS)=12 in the case of LTE/LTE-Advanced),CS(m,n) is the CS index for terminal #n and RU number #m, PN(m) is thepseudorandom number (0 to N_(CS)−1 pseudorandom numbers) for RU number#m, and Δ(n) is the CS offset value for terminal #n.

According to the CS index calculation method 2, random setting of the CSindex for each RU by using a pattern table or a pseudorandom number, forexample, can reduce the probability of increasing CM in the multipleshort sequence based SRS. Additionally, as in the CS index calculationmethod 1, the effect of reducing signaling overhead is also achieved.

CS Index Calculation Method 3

In the CS index calculation method 3, within a CS group constituted bycontinuous (or adjacent) RUs equal to the maximum number of CS (N_(CS)),different CS indexes are associated with the RUs.

FIG. 12 is a table 340 illustrating the allocation of the CS indexaccording to the CS index calculation method 3.

The table 340 in FIG. 12 shows the following example of the associationof the CS index with the RU. The maximum number of CS is “3”. RU#0through RU#2 belong to a CS group 342A, while RU#3 through RU#5 belongto a CS group 342B. In each CS group 342, different CS indexes areuniquely associated with the RUs.

The same pattern of CS indexes may be associated with different CSgroups 342. Alternatively, different patterns of CS indexes may beassociated with different CS groups 342. For example, different offsetvalues (Δ_(group)) may be used for different CS groups 342.

According to the CS index calculation method 3, different CS indexes areassociated with the RUs within the same CS group. When SRSs areallocated to continuous (or adjacent) N_(CS) RUs, the probability thatthe same CS index will be used within the band of the allocated SRSs isreduced. That is, the probability that case A, case C, and case D willoccur is reduced. It is thus possible to decrease the probability thatCM will become high. Additionally, as in the CS index calculation method1, signaling overhead can also be reduced.

CS Index Calculation Method 4

In the CS index calculation method 4, as well as in the CS indexcalculation method 3, different CS indexes are associated with RUswithin a CS group. In the CS index calculation method 4, however, a CSgroup is constituted, not by continuous RUs, but by RUs equal to themaximum number of CS (N_(CS)) formed at an interval of N_(comb) RUs.

N_(comb) is a predetermined partial band interval applied to theterminal 12. For example, if, for the purpose of reducing signaling, forexample, the partial band interval is restricted to an interval of aneven number of RUs, N_(comb) is set to be 2.

FIG. 13 is a table 360 illustrating an example of the allocation of theCS index according to the CS index calculation method 4.

The table 360 in FIG. 13 shows the following example of the associationof the CS index with the RU. N_(comb)=2, and N_(CS)=3. RU#0, RU#2, andRU#4 belong to a CS group 362A, while RU#1, RU#3, and RU#5 belong to aCS group 362B. In each CS group 362, different CS indexes are uniquelyassociated with the RUs.

The same pattern of CS indexes may be associated with different CSgroups 362. Alternatively, different patterns of CS indexes may beassociated with different CS groups 362. For example, different offsetvalues (Δ_(group)) may be used for different CS groups 362.

According to the CS index calculation method 4, different CS indexes areassociated with the RUs within a CS group formed at an interval ofN_(comb) RUs. When SRSs are allocated to RUs formed at an interval ofN_(comb) RUs, the probability that the same CS index will be used withinthe band of the allocated SRSs is reduced. That is, the probability thatcase A, case C, and case D will occur is reduced. It is thus possible todecrease the probability that CM will become high. Additionally, as inthe CS index calculation method 1, signaling overhead can also bereduced.

In the CS calculation methods according to the second embodiment, acombination of CS indexes that increases CM of SRS may be used dependingon the allocation pattern of SRSs to RUs. When conducting scheduling,the base station 10 may allocate transmit bands to RUs so that the useof combinations of CS indexes (the above-described case A through caseD) that increase CM can be avoided.

In the second embodiment, the base station 10 may dynamically inform theterminal 12 of the CS offset value by using DCI or semi-staticallyinform the terminal 12.

Instead of the base station 10 informing the terminal 12 of the CSoffset value, the CS offset value may be calculated from the ID (RNTI)of the terminal 12.

The above-described embodiments may be configured in the followingmanner.

In the multiple short sequence based SRS, when the transmission power ofthe terminal 12 has reached the maximum power, some partial bands may bedropped (not transmitted). In the multiple short sequence based SRS,decreasing the number of partial bands can reduce required transmissionpower and also decrease CM. This enables the terminal 12 to transmit SRSwith the demanded uplink transmission power.

By using the multiple short sequence based SRS, although it is notpossible to estimate the uplink channel quality in dropped partialbands, the orthogonality using CS in transmitted partial bands can bemaintained, thereby making it possible to estimate the uplink channelquality.

If SRS is generated as a result of dividing a sequence having a lengthcorresponding to the entire transmit band into partial bands, droppingof some partial bands disturb the orthogonality using CS in all thepartial bands. This makes it difficult to estimate the uplink channelquality.

In the above-described embodiments, as information to be transmitted,SRS has been discussed by way of example. However, instead of SRS,reference signals using orthogonal sequences, such as DM-RS(demodulation reference signal) and CSI-RS (Channelstate informationreference signal), may be used.

As SRS sequence data, instead of ZC sequence, GCL (Generalized ChirpLike) sequence, M sequence, Computer generated CAZAC sequence used whensignal bandwidth is 1 RB or 2 RBs in LTE/LTE-Advanced system may beused.

The embodiments of the present disclosure have been discussed above. Themodes of the above-described embodiments may be combined in any manner.

The present disclosure may be implemented by software, hardware, orsoftware operating together with hardware. The functional blocksutilized for describing the above-described embodiments may entirely orpartially be implemented by an LSI, which is one example of integratedcircuits. The processes discussed in the above-described embodiments mayentirely or partially be controlled by one LSI or a combination of LSIs.An LSI may be constituted by individual chips or by one chipimplementing all or some of the functional blocks. An LSI may includedata input and output. An LSI may be called an IC, a system LSI, a superLSI, or an ultra LSI, depending on the integration degree. Theintegration of the functional blocks and processes is not necessarilyimplemented by using an LSI. Instead, a dedicated circuit, ageneral-purpose processor, or a dedicated processor may be used. A FPGA(Field Programmable Gate Array) that is programmable after an LSI ismanufactured, or a reconfigurable processor that may reconfigureconnections or settings of circuit cells within an LSI may be used. Thepresent disclosure may be implemented as digital processing or analogprocessing. Due to the progress of semiconductor technologies or theappearance of a derivative technology, if a circuit integrationtechnology which replaces an LSI technology is developed, the functionalblocks may be integrated by utilizing such a technology. The applicationof a biotechnology, for example, may be one of such cases.

A terminal of the present disclosure includes a circuit and atransmitter. The circuit specifies a frequency domain to be used fortransmitting a reference signal using predetermined sequence data andapplies a phase shift index associated with the specified frequencydomain to the reference signal. The transmitter transmits the referencesignal to which the phase shift index is applied by using the specifiedfrequency domain.

In the terminal of the present disclosure, a random phase shift index isassociated with each of a plurality of frequency domains.

In the terminal of the present disclosure, the random phase shift indexis an index calculated based on a predetermined pseudorandom number.

In the terminal of the present disclosure, a phase shift index isassociated with each of a plurality of continuous frequency domains. Thephase shift indexes associated with the plurality of continuousfrequency domains are different from each other.

In the terminal of the present disclosure, the phase shift index is anindex calculated based on an ID which varies among terminals.

In the terminal of the present disclosure, the phase shift index is anindex calculated based on an offset value supplied from a base station.The offset value varies among terminals.

A base station of the present disclosure includes a receiver and acircuit. The receiver receives a reference signal using predeterminedsequence data in a specific frequency domain. The circuit compares abase signal and the reference signal with each other. The base signal isa signal to which a phase shift index associated with the specificfrequency domain is applied.

A communication method of the present disclosure includes: specifying afrequency domain to be used for transmitting a reference signal usingpredetermined sequence data and applying a phase shift index associatedwith the specified frequency domain to the reference signal; andtransmitting the reference signal to which the phase shift index isapplied by using the specified frequency domain.

A communication method of the present disclosure includes: receiving areference signal using predetermined sequence data in a specificfrequency domain; and comparing a base signal and the reference signalwith each other. The base signal is a signal to which a phase shiftindex associated with the specific frequency domain is applied.

The above-described embodiments have been provided for the purposes ofillustration and description of the present invention. It is notintended to be exhaustive or to limit the scope of the invention to theembodiments. Those skilled in the art may carry out the invention invarious other modes without departing from the spirit and scope of theinvention.

An embodiment of the present disclosure is suitably used in a mobilecommunication system.

REFERENCE SIGNS LIST

10 base station

11 circuit

12 terminal

13 circuit

20 receiver

21 antenna

22 demodulator-decoder

24 SRS extractor

26 quality estimator

28 scheduler

30 replica generator

32 CS index calculator

34 SRS resource storage

36 SRS control signal generator

38 modulator-coder

40 transmitter

60 receiver

61 antenna

62 demodulator-decoder

64 CS index calculator

66 SRS generator

68 SRS band setter

70 modulator-coder

72 transmitter

The invention claimed is:
 1. A terminal comprising: circuitry, which, inoperation, specifies a frequency domain among a plurality of frequencydomains to be used for transmitting a reference signal usingpredetermined sequence data, determines a phase shift index by adding aphase shift offset value to a phase shift index associated with thespecified frequency domain, and applies the determined phase shift indexto the reference signal, wherein each of the plurality of frequencydomains is associated with a respective phase shift index; and atransmitter, which, in operation, transmits the reference signal towhich the determined phase shift index is applied by using the specifiedfrequency domain.
 2. The terminal according to claim 1, wherein a randomphase shift index is associated with each of the plurality of frequencydomains.
 3. The terminal according to claim 2, wherein the random phaseshift index is an index calculated based on a predetermined pseudorandomnumber.
 4. The terminal according to claim 1, wherein a phase shiftindex is associated with each of a plurality of continuous frequencydomains, and the phase shift indexes associated with the plurality ofcontinuous frequency domains are different from each other.
 5. Theterminal according to claim 1, wherein the circuitry, in operation,determines the phase shift offset value based on an ID of the terminal.6. The terminal according to claim 1, further comprising: a receiver,which, in operation, receives the phase shift offset value from a basestation, wherein the base station transmits different phase shift offsetvalues to terminals.
 7. A base station comprising: a receiver, which, inoperation, receives a reference signal using predetermined sequence datain a specified frequency domain among a plurality of frequency domains,wherein each of the plurality of frequency domains is associated with arespective phase shift index; and circuitry, which, in operation,generates a base signal, compares the base signal and the referencesignal with each other, and estimates a quality of an uplink channelbased on the comparison of the base signal and the reference signal witheach other, wherein the base signal is generated by determining a phaseshift index by adding a phase shift offset value to a phase shift indexassociated with the specified frequency domain, and applying thedetermined phase shift index to the reference signal.
 8. A communicationmethod comprising: specifying a frequency domain among a plurality offrequency domains to be used for transmitting a reference signal usingpredetermined sequence data, wherein each of the plurality of frequencydomains is associated with a respective phase shift index; determining aphase shift index by adding a phase shift offset value to a phase shiftindex associated with the specified frequency domain; applying thedetermined phase shift index to the reference signal; and transmittingthe reference signal to which the determined phase shift index isapplied by using the specified frequency domain.
 9. A communicationmethod comprising: receiving a reference signal using predeterminedsequence data in a specified frequency domain among a plurality offrequency domains, wherein each of the plurality of frequency domains isassociated with a respective phase shift index; generating a base signalby determining a phase shift index by adding a phase shift offset valueto a phase shift index associated with the specified frequency domain,and applying the determined phase shift index to the reference signal;comparing the base signal and the reference signal with each other; andestimating a quality of an uplink channel based on the comparing of thebase signal and the reference signal with each other.